1. Field of the Invention
The invention relates to a data transmitting apparatus, a receiving apparatus, and a data transmission and reception system for recording digital data which is transmitted via, for example, a digital satellite broadcasting onto a storage medium.
2. Description of the Related Art
Recently, a digital broadcasting system for transmitting multimedia data such as image signal, audio signal, and the like by using a communication satellite has been being put into practical use. The invention can be applied to such a digital broadcasting system. FIG. 4 shows an outline of a typical digital broadcasting system. The transmission side of a program is made up of an up-link station, a program provider, and a management system.
Video and audio data from a program provider 101 is supplied to an encoder and multiplexer 103 of the MPEG (Moving Pictures Expert Group) 2 of an up-link station 102. In the MPEG 2 encoder and multiplexer 103, the video and audio data is compressed and the compressed video and audio data is stored in a packet of a length of 188 bytes. A plurality of programs and the packets of the respective corresponding video and audio data are multiplexed, so that a transport packet of the MPEG2 is formed. A transport stream is formed by a series of transport packets. The number of transport streams corresponds to the number of transponders installed in the communication satellite.
The MPEG2 transport stream is supplied to a transmission system 104. In the transmission system 104, processes such as scrambling process of every packet, error correction encoding of every packet, modulation, and the like are executed and a modulation output is supplied to a transmitting antenna 105. The scrambling process is necessary to realize a conditional access which is used to control about the permission or inhibition of the monitoring every viewer. In the scrambling process, for example, a contract of a pay-per-view in which only a certain program is monitored with a toll every time can be made. A key to descramble is supplied from a key management system 106 to the MPEG2 encoder and multiplexer 103 and has been inserted as one of the packets into the transport stream in a manner similar to the video and audio information.
An integrated management of the MPEG2 packets is performed by a program management system 107. The program management system 107 and key management system 106 are unified, thereby encrypting the key to descramble. Further, in a customer management system 108, items regarding a monitor contract or the like are managed. Viewer information is transmitted and received betweem the customer management system and the home of the viewer via a telephone line 109.
A broadcasting radio wave transmitted from the transmitting antenna 105 through a communication satellite 110 is received by a receiving antenna 111 at each home. A receiver 112 is connected to the receiving antenna 111. The receiver 112 is constructed by a tuner for designating a receiving transponder, a demodulating unit, a descrambling unit for descrambling, a demultiplexer for designating a packet to be separated, a video decoding unit, an audio decoding unit, and the like. The decoded video and audio signals are supplied to a television receiver 113.
A key for descrambling is encrypted and transmitted as concerned information together with video and audio signals. The key to decrypt the encryption has been stored in an IC card 114 inserted in the receiver 112. Which program can be descrambled can be controlled from the transmission side on the basis of contract-information of each reception system. The receiver having a conditional accessing function is usually called an IRD (Integrated Receiver/Decoder).
The above digital satellite broadcasting system is not limited to an application field such that a television broadcasting is merely monitored but can be also used as a transmission system of digital data of a large capacity by many channels. That is, the receiver of the digital satellite broadcasting can have a function as a receiving apparatus of digital data such as video and audio data, data for a computer, or the like.
As one of using methods of the digital satellite broadcasting, there is considered a method whereby by combining a receiver and a recording medium of a large capacity, a large quantity of reception data can be accumulated. For example, the reception data is recorded at night when a transmitting line is relatively free, and a desired portion is reproduced from the recorded data later. As a recording medium of a large capacity, a digital VCR, a hard disk, an optical disk, a semiconductor memory, or the like can be used.
In the digital satellite broadcasting, although a form in which a monitor contract is made on a channel unit basis, a form (pay-per-view) in which a fee of only the monitored programs is paid, and the like exist, it is-generally a toll broadcasting and the conditional access is used. Therefore, according to the method whereby reception data has previously been stored in the memory of the large capacity and the desired program is reproduced later, it is irrational that all of the programs which are stored are charged. The programs which were selectively read out from the memory and were reproduced are charged.
The monitor control in the toll broadcasting system is performed by a scramble authorization system. In this system, individual information (EMM: Entitlement Management Message) that was formed on the transmission side and is peculiar to the receiving terminal is sent to the viewer. On the receiving terminal, the EMM of the same ID as the own ID is decrypted, and a work key is fetched into the IC card. The key to decode the EMM is a key which is individual for each receiving terminal and has previously been stored in the IC card. Further, a contracted channel ID and a contract type (temporary contract, pay-per-view, or the like) in addition to the work key are included in the EMM.
When a program is monitored, common information (ECM: Entitlement Control Message) which is accompanied with the program and is common for the receiving terminals is fetched into the IC card. If the work key corresponding to this channel has previously been stored, a descrambling is performed and can be monitored. The EMM and the common information (hereinafter, referred to as an ECM) are transmitted in a form of the packet of the transport stream of the MPEG2 in a manner similar to the video and audio data. In case of the pay-per-view, the monitor information is periodically up-loaded through the telephone line.
In the foregoing toll broadcasting system, as one of methods of realizing a method whereby the recording medium (large capacity memory) is combined to the receiver and a desired one of the programs stored in the recording medium is selectively reproduced and only the reproduced program is charged, a method of recording the EMM and ECM as well to the recording medium is also considered. The video and audio data of a plurality of programs are recorded in a scrambled state (form of the packet) on the recording medium, the video and audio data which was selectively reproduced is descrambled by the system of the receiver, and is further decoded. In order to enable the descrambling, the EMM and ECM are recorded to the recording medium.
However, a time lag exists between the timing when recording the reception data to the recording medium and the timing when reproducing it later. There is a possibility such that the EMM which is individual for each receiving terminal is changed due to a change or the like in contract. Thus, according to the system for recording the EMM at that time point together with the data of the program, there occurs a fear such that the reliability of the conditional access is deteriorated. For example, upon recording, although the customer which is instructed in the EMM has a right corresponding to the rank of the recorded program, at the time of point of reproduction, even if the right has already been terminated due to the elapse of the validity term, the right is authorized on the EMM which has already been recorded. In an extreme case, a situation such that the right which was validated by the latest EMM is invalidated by the reproduced old EMM also occurs.